The invention relates generally to rectifier circuits, and more particularly, to circuits having a feedback signal for producing substantially linear operation of rectifying diodes.
There are many types of circuits for providing power to a load. Many such circuits include a rectifier circuit for receiving an alternating current (AC) signal and providing a direct current (DC) output signal. In one application, a ballast circuit for energizing a fluorescent lamp includes a rectifier circuit having an input coupled to a relatively low frequency AC power source and a DC output coupled to an inverter circuit. The inverter circuit applies a relatively high frequency AC signal to the lamp that is effective to cause a predetermined level of current to flow through the lamp and thereby produce visible light.
Rectifier circuits generally contain one or more rectifying diodes coupled so as to form input (AC) and output (DC) terminals. In operation, each of the rectifying diodes is conductive for a part of the AC input signal. For example, a first rectifying diode may be conductive for a part of the positive portion of the AC input signal and a second rectifying diode may be conductive for a part of the negative portion. One problem associated with this arrangement is that the diodes which form the rectifier circuit do not operate in a linear manner. Typically, the rectifying diodes are only forward biased, i.e., conductive, when the AC input signal is at or near its peak value. The non-linear operation of the rectifying diodes has a negative impact on the efficiency of the circuit since only a limited amount of power from the AC power source is available to the circuit. Further, the total harmonic distortion (THD) and the power factor (PF) of the circuit are also adversely affected.
It would, therefore, be desirable to provide a circuit including a rectifier having rectifying diodes that are operated in a substantially linear manner.